In manufacturing semiconductors, impurities are sometimes introduced to the semiconductor base material through a process known as "doping." Doping permits the fabrication of n-type or p-type semiconductors with varying degrees of conductivity. In general, the greater the extent of doping, the higher the conductivity of the semiconductor device.
Dopants are often introduced to the process in the form of gases. These gases are used to deposit or remove materials on the surface of the semiconductor device in order to provide insulating regions and connective features required by the semiconductor architecture. The gases used during these processes include, among others, HCl, HBr, tungsten hexafluoride, and silane. These gases are extremely toxic and/or corrosive and/or pyrophoric (i.e., may explode or burn upon contact with an oxidizer such as room air), and therefore must be carefully controlled and contained within gas conduit systems that are leakproof.
When dealing with these semiconductor gas conduit systems, it is advantageous to minimize the area contacted by the gases (the "wetted surface area") so as to reduce or minimize contamination of the gases. Contamination typically occurs as a result of water vapor which desorbs from the surfaces of the gas conduit and control components. This contamination is typically introduced at the time of installation or following maintenance operations that expose the wetted surface areas to air.
Furthermore, because welded surfaces alter the surface chemistry and have an inherent propensity to corrode, it is advantageous to minimize the number and size of welded surfaces within the gas conduit system.
One method of achieving the dual objectives of reducing surface area and reducing the number and size of welded surfaces is described in U.S. Pat. No. 5,836,355 issued to Markulec et. al. on Nov. 17, 1998. The '355 patent relates to an integrated gas conduit system or "gas panel" which includes a series of linear assemblies each comprising a plurality of interconnected, discreet blocks. The blocks are coupled such that one or more ports within each block is in fluid communication with one or more ports of another block or blocks such that a pressurized fluid may flow therebetween. Metal gaskets disposed between the blocks and around the ports form an effective seal, thus containing the fluids therein. Threaded rods or bolts passing longitudinally through the blocks secure each linear assembly.
While the '355 patent provides a gas panel which minimizes welds and wetted surface area, the discreet blocks that make up the panel must be precisely aligned in order to prevent leakage. Referring to FIG. 9, the gas panel is comprised of two layers of linear block assemblies 600 and 700, one layer oriented transversely to the other. One or more discreet blocks 601 may have porting to not only adjacent blocks 602, 603 within the linear assembly, but also to other blocks 701 mounted transversely thereto. In order to ensure effective sealing at all interfaces, it is critical that the individual linear assemblies 600, each comprised of a plurality of blocks, ports 605, metal gaskets 604, and bolts 606 (the latter required to compress and seal the blocks and gaskets), be aligned precisely not only along their longitudinal or "x" axis but transversely as well (the "y" and "z" axes). Each block of each linear assembly 600 is dimensionally similar such that alignment of the outside surfaces 607 ensures alignment of the internal porting 605.
Many times the blocks are difficult to align and, unfortunately, even slight misalignment can result in gasket leakage. For example, if two adjacent blocks 601 and 602 of the linear assembly 600 are misaligned along the z axis by 0.005 inches and the assembly 600 is subsequently bolted to the two blocks 701 and 702 of two transverse assemblies 700, the act of bolting the blocks 601 and 602 to the assemblies 700 (using the bolts 608) will force the lower faces of the blocks 601 and 602 to the mating faces of the blocks 701 and 702 respectively. Due to the misalignment between the blocks 601 and 602, a shear strain on the metal gasket between those blocks will develop. When metal gaskets of this type are sheared, seal integrity is sacrificed. The effects of even partial seal failure include: compromising the semiconductor process; damaging gas system components; and potentially inflicting serious injury or even death to system operators.
Accordingly, a clamping device that can precisely align the blocks in the y and z directions is advantageous to produce these linear assemblies. At the same time, the device must permit relative motion between the blocks of the linear assembly (i.e., in the x direction) so that they may draw together and compress the metal gaskets. Currently available alignment methods use various devices to clamp the blocks between two faces before bolting. These devices, however, do not always produce a repeatable clamp force. If the clamp force exerted on the blocks is not repeatable, the frictional forces between the blocks and the clamp are likewise not repeatable. If the clamp force is too high, the frictional forces on the blocks will prevent the blocks from drawing together and forming a hermetic seal. If the clamp force is too low, the act of torquing the bolts 606 will induce a torsional moment into the linear assembly, resulting in sheared gaskets and misaligned blocks. Unfortunately, the need to minimize the frictional forces on the blocks is at odds with the need to sufficiently restrain the blocks during torquing.
Another problem with conventional clamping devices is that the clamp devices have only one point of loading. Thus, if the blocks are placed off-center from the loading point, the clamping faces will become skewed (i.e., not parallel). This will also produce a variation in the clamp load applied and adversely impact alignment and sealing.
Accordingly, what is needed is a way to apply a consistent and predictable clamping force to a group of objects while maintaining precise alignment therebetween. What is further needed is a device that can apply such a clamping force without overly restricting relative motion of the objects transverse to the clamping force.